Catheters are used in a variety of minimally invasive medical procedures. A major portion of the catheter field involves catheters that track over a guidewire, such as angioplasty catheters that are used to advance an inflatable member over a guidewire to a desired vascular location. One advancement in this field has been the use of rapid exchange catheters in place of standard over-the-wire catheters.
A standard over-the-wire catheter typically tracks over a guidewire over its entire length such that, in order to maintain a distal guidewire location while exchanging the catheter, a guidewire extension or very long guidewire is used. To exchange the standard over-the-wire catheter, the guidewire is held in place while the catheter is withdrawn. The proximal end of the guidewire is held until the distal end of the catheter exits the patient's body, while the distal end of the guidewire remains in the desired location, meaning that the guidewire, during exchange, must be twice as long as the catheter.
A rapid exchange catheter tracks over the guidewire for only a short distal portion of the catheter. Examples of rapid exchange catheters, their use, and methods for making such catheters are illustrated by Williams et al. in U.S. Pat. No. 6,409,863, the disclosure of which is incorporated herein by reference. The catheter shown by Williams et al. includes an outer member and a distally located inner member, with a balloon proximal end attached to the distal end of the outer member and a balloon distal end attached to the distal inner member. A proximal guidewire port is located distal of the proximal end of the catheter, with the distal inner member opening at its proximal end to the proximal guidewire port, and extending to the distal end of the catheter.
One difficulty which can arise with some rapid exchange catheters is that an inner member defining the distal guidewire lumen may allow passage of fluid therethrough. Because the proximal guidewire port is typically in view of fluoroscopic instruments, passage of contrast fluid used to visualize the treatment location (for example, the location of a lesion in a blood vessel) proximally through the guidewire lumen can be misinterpreted as indicating device failure during inflation of a distally located balloon. Reducing the diameter of the guidewire lumen to prevent fluid passage, however, can make it more difficult to push the catheter over the guidewire. Reducing the slidability of the catheter with respect to the guidewire (and vice-versa) can make it more difficult to maintain and manipulate guidewire position, thereby making the physician's task of advancing a catheter over the guidewire more difficult.